In a conventional carriage-style printer, the paper (or other recording medium) is successively advanced such that a portion of the paper is located within a print zone. While the paper is held stationary, a printhead is moved along the print zone in a direction that is substantially perpendicular to the paper advance direction, and marks are made by the printhead on the paper in the print zone as the printhead moves past.
An example of such a carriage style printer is an inkjet printer, where the printhead includes an array of nozzles arranged in a direction substantially parallel to the paper advance direction, and the print zone within which printing may be done corresponds to the region between the two endmost nozzles in the array. The printhead and at least a portion of the ink supply for the printhead are typically located on a carriage which moves back and forth along a carriage guide rail. In a commonly used printer architecture, the print zone is horizontal and the printhead nozzles are located vertically above the paper in the print zone. For good image quality, it is important to keep the nozzles at a constant distance from the paper in the print zone. This means that 1) the carriage should be mounted at such an angle that the two endmost nozzles are substantially the same distance from the print zone, and 2) the carriage guide rail should be straight and substantially parallel to the print zone.
In conventional carriage-style printers, the carriage guide rail is a precision ground steel round rod, and the carriage includes a corresponding rounded recess which rides along the round rod. The carriage guide rail bears the weight of the carriage and is primarily responsible for the accurate travel of the carriage. A second rail, the anti-rotation rail or slider rail, is used to make contact with a second part of the carriage in order to fix the carriage rotational orientation about the carriage guide rail axis. The anti-rotation rail may be a second round rod, but it may be made more cost effectively out of sheet metal (see, for example, U.S. Pat. No. 5,368,403). While this round rod design works well, the precision ground steel round rod is more expensive than desired. Therefore, it is desirable to form not only the anti-rotation rail, but also the carriage guide rail using sheet metal.
U.S. Pat. Nos. 6,520,633 and 6,742,865 describe a variety of carriage guide rail (or track) configurations made from formed, bent or extruded metal or plastic. In each of the rail configurations, a recess (or receptor groove) is formed in the carriage with a configuration sized and shaped to correspond to the rail configuration. The rail and receptor groove configurations can be undesirably complex and/or require too much space in the printer.
In another prior art carriage guide rail formed of bent metal, the rail has a bottom horizontal wall and a vertical wall extending up from the horizontal wall, and the carriage has a projection which rides on the horizontal wall and the vertical wall. However, gravity tends to rotate the carriage in such a way as to tend to pull the projection out of contact with the vertical wall, so that a bias spring is required in order to keep the projection against the vertical wall.
Thus, for a low-cost printer to have improved image quality, there is a need for an improved carriage guide rail configuration which enables low cost, compact design, reduced complexity in carriage and rail design, uniform printhead to print zone spacing, low wear, and stable carriage motion.